In recent times, sustained performance effected over a longer period than ever is required for non-aqueous electrolyte secondary batteries, such as lithium (ion) secondary batteries, which are used for drive power sources (on-vehicle power source) for vehicles, such as hybrid vehicles, electric vehicles and fuel cell vehicles. Thus, in order to suppress the deterioration of a battery capacity to improve the cycle characteristics and high rate characteristics, the addition of boron-containing lithium salt, such as lithium bis(oxalato)borate (Li[B(C2O4)2]; the so-called LiBOB), phosphorus-containing lithium salt, such as lithium difluorobis(oxalato)phosphate (Li[PF2(C2O4)2]; the so-called LPFO) or an appropriate carbonate compound to a non-aqueous electrolyte has been being employed widely.
For example, Patent Document 1 discloses a lithium secondary battery comprising a non-aqueous electrolyte containing boron-containing lithium salt, which is referred to as LBFO in the same document, at a predetermined concentration in the solution or at a predetermined molar ratio with respect to an electrolyte (LiPF6).